Development and Validation of a Simple, Rapid and Accurate Rp-HPLC Method for the Estimation of Favipiravir in Bulk Drug and Marketed Pharmaceutical Formulation

Favipiravir, a pyrazine-carboxamide inhibitor of viral RNA-dependent RNApolymerase, requires a simple and reproducible chromatographic assay for routine quality control ofbulk drug and finished dosage forms. A reverse-phase high-performance liquid chromatographicmethod was therefore developed, optimised and validated in accordance with ICH Q2(R1).Separation was achieved on an Agilent 1260 Infinity system fitted with a C18 (2) 250 × 4.6 mm, 5µm column, using methanol and 0.02 M potassium dihydrogen orthophosphate buffer (75:25 v/v, pH3.5) as the mobile phase at a flow rate of 1.0 mL/min, an injection volume of 20 µL, a columntemperature of 30 °C and photodiode-array detection at 220 nm. Preliminary trials with methanol–water (75:25 v/v) produced peak broadening, and adjustment of that mobile phase to pH 3.0produced fronting and splitting; substitution of phosphate buffer for water at pH 3.5 gave a singlesymmetrical peak. Under the final conditions favipiravir eluted at 3.6 min with a capacity factor of1.56, 6,668 theoretical plates and a tailing factor of 1.03. The detector response was linear from 10 to70 µg/mL with a correlation coefficient of 0.9998 and %RSD of 1.08–1.49 across five replicateinjections at each level. Recovery determined by standard addition at 80%, 100% and 120% was99.47–100.30% (mean 99.94%), with %RSD of 0.78–1.18. Repeatability over six injections of a 20µg/mL solution gave %RSD 0.89, while intra-day and inter-day precision at 20, 30 and 40 µg/mLgave %RSD of 0.32–0.79 and 0.32–1.02 respectively. Deliberate variation of mobile-phasecomposition (±1% v/v), pH (±0.1), flow rate and column temperature gave %RSD of 0.28–0.79, andanalysis by two analysts gave 100.78 ± 0.40% and 100.22 ± 0.78%. The limit of detection and limitof quantitation were 0.45 and 0.60 µg/mL. Applied to bulk drug the method gave 99.86 ± 0.78% ofthe amount taken, and applied to a marketed 200 mg tablet formulation it gave 99.87 ± 0.73% of thelabel claim, with no evidence of excipient interference. The method is simple, rapid, economical andsuitable for routine assay and quality-control analysis of favipiravir.